Inner axel seal leak?

Some possible causes;

The seal has a spring tensioner, it can pop out of place when installed. (I coat them in axle grease to help them stay in place when tapping the new seal in)

Seal damaged during installation and / or installed with the wrong side out.

Seal cocked in the bore.

Axle weight left on the seal lip during installation , removal or left hanging loose during a center gear set swap.